Not all babies experience sleep regressions at four months, but research has shown that there is a considerable amount of individual variation in the sleep of babies. While some babies may not have detectable sleep regression at four months, others may have difficulty sleeping at this age or at a point earlier or later. A popular theory suggests that young children go through exactly 10 difficult periods of restlessness followed by leaps in growth, but the evidence is not as clear. It is hard to say whether an attack of irritability is due to a “regression of sleep” or simply because a baby is a baby.
In 1974, Robert Horwich, an animal researcher at the Chicago Zoological Society, noticed that several baby members of 12 different primate species from two Chicago zoos tended to change their lactation habits (sometimes by breastfeeding more, sometimes breastfeeding less) at about the same time as others. He called the phases of intensified lactation “regressive periods”, defining them as a time during which babies returned to a level of need and attachment that they had previously overcome. More than a decade later, in the mid-80s, a research team of husband and wife psychologists from the Netherlands, Dr. Van de Rijt published that study in the peer-reviewed Journal of Reproductive and Infant Psychology.
That same year, they released their new book, “The Wonder Weeks”, which cataloged exactly when each of the 10 leaps would occur and the difficult behaviors and developmental milestones they would coincide with; and what activities parents should do with their babies to convince those skills to develop or help them feel safe as they explore in new ways. Critics say that 15 participants and two direct observations are too small a set to base a theory on. “To make it convincing” said Dr. Jodi Mindell, Ph.
D., “I think that means looking at thousands of babies”. In a video on the Wonder Weeks website, Dr. Plooij stated that subsequent investigations confirmed the timed jumps. In the early 2000s, researchers from universities in Spain, England and Sweden tried to replicate the 1992 results in three different studies involving a total of 66 babies.
Plooij argued that these studies produced similar findings to his own. The important question for parents is how to help their babies sleep more? Exhausted parents should stay firm in their routine and not change it too quickly out of frustration. Parents can always bathe their baby before bedtime, for example, or spend time curled up in a cozy chair with the lights dimmed. Why do babies have a 4-month sleep regression? However, not all babies experience it.
For those who do, it may come a month or so sooner or later. Not all babies go through 4-month sleep regression; I have seen many babies overcome this phase of development with little disruption of their sleep. The 12-month sleep regression is actually the same as the 11-month regression, although if your toddler starts is in the twelfth month, you may actually transition to just a nap earlier.